ESXi host Not Responding in vCenter due to routing conflicts after adding VMkernel adapters

Products

• VMware vSphere ESXi

Issue/Introduction

• ESXi hosts appear in a "Not Responding" or "Disconnected" state in the vCenter Server inventory.
• The issue occurs immediately after adding a new VMkernel adapter (e.g., vmk3) for backup or alternative traffic.
• Management traffic (vmk0) can reach the vCenter Server IP address.
• `vmkping` from vmk0 to vCenter would succeed, but standard `ping` from the host fails.
• Routing table verification shows the default route has shifted to the newly created VMkernel interface.
  
• VMkernel adapter was created at dvswitch by following the procedure
  DVSSwitch-->Portgroup--> Add VMkernel Adapter 
  
• The option "Configure on TCP/IP Stack" was selected when assigning an IP to the VMK in the IPV4 Settings
  

Cause

• The option Configure on TCP/IP stack overwrites the default route with the newly added VMK adapter's  network gateway.
• If the new adapter's gateway is mapped to route default traffic, and that path cannot reach the vCenter Server address, communication between the host and vCenter drops.

Resolution

• To restore management connectivity, ensure that default traffic is explicitly routed to the Management Network's gateway (typically vmk0).

• •  Log in to the ESXi host via SSH or the ESXi Shell.
  • Check the current routing table by running:
        `esxcfg-route -l`
  • Identify the original Management Network gateway IP (associated with vmk0).
  • Reroute the default route to the original Management Network gateway using the following command:
        `esxcli network ip route ipv4 add --gateway ####.####.####.#### --network default` 
        *(Note: Replace ####.####.####.#### with the actual Management Gateway IP address identified in step 3.)*
    
    
  •  Verify the communication by pinging the vCenter Server from the host shell:
        `ping <vCenter_IP_Address>'


  • Check if the ESXi is showing in the vCenter's inventory.

 

• To avoid the issue from happening -

• • Either configure VMK individually on every ESXi host and check the option "Override default gateway for this adapter" and mention the gateway of that network.
    
    
    Or
    
    
  • Select the option "Configure On VMkernel Adapter" instead
    

Additional Information

Configuring static routes for vmkernel ports on an ESXi host
Create a VMkernel Adapter on a vSphere Distributed Switch